Technical Field
The present invention relates to an austenitic steel matrix-nanoparticle composite and a producing method thereof.
Related Art
In recent years, there has been a demand for development of a high-strength material for the purpose of improvement in fuel efficiency of a vehicle, reduction in exhaust gas of a vehicle, and absorption of a collision impact of a vehicle or prevention of a damage of a vehicle body. Accordingly, a high-strength steel material capable of achieving a decrease in thickness of a vehicle body through an increase in strength of a vehicle body material and supporting a greater weight by a smaller volume to decrease the weight of the vehicle body has been actively developed.
High-strength steel sheets for a vehicle which are mainly used these days have a tensile strength of 780 MPa or more. However, since an elongation percentage rapidly decreases with the increase in strength and the increase in strength of a steel sheet causes a decrease in moldability, there are problems in that it is difficult to manufacture vehicle components with complicated shapes and the manufacturing process extends even when the same component is manufactured.
Therefore, there is a demand for a steel sheet with a high strength of a tensile strength of 780 MPa or more and with an excellent elongation percentage. With this demand, various composite steel sheets of ferrite-martensite double-phase steel (DP steel) or transformation induced plasticity (TRIP) steel using transformation induced plasticity of residual austenite, or the like have been developed.
In this regard, Korean Patent Application Laid-open No. 10-2008-0065294 discloses a steel material with a high austenite crystal coarsening temperature which includes carbon of less than 0.4 wt %, aluminum of less than 0.06 w %, titanium of less than 0.01 wt %., niobium of 0.01 wt %, vanadium of less than 0.02 wt %, and fine oxide particles of silicon and iron with an average precipitate size of less than 50 nanometer which are distributed in the whole steel microstructures of 5 nanometer to 30 nanometer.